Wireless data and telephony communication systems are quickly replacing conventional communication systems. Conventional terrestrial wireless telephony relies on unobstructed Line-Of-Sight (LOS) paths or close range multipaths between the sending and receiving stations. This technology is easy to maintain. However, the communication range of operation is limited. The LOS restriction is particularly important for special mobile units, such as off-road vehicles. The local terrain quite often dictates vehicle position relative to the sending and receiving units in order for unobstructed communication to occur. Also, land-based wireless infrastructures are expensive to deploy and maintain, especially in remote areas.
Present wireless communication systems fail to provide broadband wireless communication in real time across extended distances while maintaining a LOS path between stations where one or both stations may be in motion. Many regions of the world today have a sparse or no fixed communication infrastructure and lack the resources needed to upgrade their existing equipment to match more developed areas. Wireless communication systems are an effective tool for providing this service. However, present wireless systems fail to meet the needs of specific applications.
A factor impacting traditional wireless communication infrastructures is the huge increase in demand for communicating broadband services consisting of voice, video, and data information. Because of inherent limitations in the transmission media, wireless communication must compensate for noise introduced in the radio path. The following are wireless techniques for compensating for noise: 1) restricting the range; 2) increasing the transmitted signal amplification or power; 3) increasing the received signal amplification; 4) increasing the error correcting efficiency; 5) changing the radio signal modulation or frequency to reduce the impact of noise; or 6) a combination of any or all of these techniques. However, all of these techniques affect the cost and complexity of a wireless system. Moreover, compensating for unreliable wireless paths becomes increasingly difficult as the data rate increases.
Various satellite-based solutions have been proposed to address the above identified issues, but are generally too costly unless applied over continental or larger geographic areas. Low Earth Orbit (LEO) and Medium Earth Orbit (MEO) based systems aspiring to global coverage do so at the expense of operating satellites over the two thirds of the earth covered by water. Additionally, the often huge increase in wireless earth-space-earth path distance between terrestrial stations adversely impacts satellite-based solutions because of the end-to-end transmission delay and increased path loss. Thus, real-time communication is impractical at higher orbital altitudes. This is especially the case with Geosynchronous Earth Orbit (GEO) satellite systems. The following are other drawbacks or implementation difficulties of GEO satellites: 1) the high cost of launching the satellites into the geostationary orbit; 2) long inter-satellite link distances; and 3) high transmit power requirement. Neither satellite-based or fixed land-based systems easily facilitate transient demands for communication in remote areas. Presently, no communication infrastructure exist for allowing economic operation within a relatively confined geographical area for service that may have fluctuating demand and require rapid deployment of the system.
Another concern in a wireless communication infrastructure is effective radio frequency spectrum management. Satellite-based systems must contend with an increasingly crowded available spectrum and complex and expensive international licensing procedures. This is especially the case for LEO and MEO satellite systems that operate worldwide but are constrained to use a single fixed frequency allocation for communications from and to terrestrial stations. Often this forces a system design into nonoptimum frequency bands which can seriously impact the cost of the system.
The LEO and MEO satellite communication systems attempt to mitigate the GEO disadvantages. However, LEO/MEO satellite networks require a significantly greater number of satellites to provide global coverage. As an example, the IRIDIUM.RTM. LEO satellite network proposed by Motorola Inc. and ODYSSEY.RTM. MEO satellite network proposed by TRW are targeted to become worldwide, satellite-based, cellular systems primarily intended to provide commercial low-density, narrowband mobile service via portable user units. Similar LEO and MEO satellite networks are being proposed, but they too focus primarily on providing narrowband communication to cellular users. Recently, several "Big LEO" satellite systems are targeting toward providing broadband service primarily to stationary terminals. Teledesic.RTM. (Teledesic Corp.) is one such system that proposes to orbit an LEO communications system consisting of 840 satellites featuring fixed-earth cells and fast-packet switching onboard each inter-networked satellite. A major challenge to this type of approach is the enormous cost of placing the satellites in orbit prior to developing the subscriber base for recovering the initial investment or validating the network operating costs.
Accordingly, there is a need for a low-cost, easily maintainable, fast deployable communication system capable of broadband and network communication in various environments. The present invention is directed to providing such a communication system.